The discovery of an original document proving the late prince Bernhard’s membership of the Nazi party revealed in a recently published book, has prompted some MPs to request an investigation into his past affiliation with the party.

Prince Bernhard, the current king’s grandfather, had always denied membership, even when a copy of his membership card was found in the United States, where the original document had been kept by the Americans, some thirty years ago. His membership was terminated in 1936, the year he got engaged to heir to the Dutch throne, Juliana.

King Willem-Alexander has not given an official reaction yet but the royal press service has confirmed the existence of the card and provided a copy.

In an earlier interview, biographer Annejet van der Zijl said the publication of the existence of the card was a “feather in the cap” of the royal family, implying that the king knew about the find and had no objections to its being made public.

Caretaker prime minister Mark Rutte told journalists the find is “confrontational” but that he feels a government investigation is unnecessary because the fact of the prince’s membership had been common knowledge for some time.

He also said said all the information is there and it’s the historians’ task to do something with it.

The membership card was found by royal archive chief Flip Maarchalkerweerd, who mentions the fact in a footnote, the bulk of his book De Achterblijvers (Those who stayed behind) being concerned not with Bernhard but with the flight of  then queen Wilhelmina to England to lead a government in exile when the Germans occupied the Netherlands.

Open secret

D66 MP Alexander Hammelburg, who is Jewish, and who requested the investigation, said prince Bernhard’s membership of the NSDAP was an “open secret” but merited “serious investigation” nevertheless.

Israel information and documentation centre CIDI has said it would support an investigation saying the prince’s denial had been “painful”. “It is now important to get all the information out,” director Naomi Mestrum told broadcaster NOS.

The NIOD institute for Holocaust and genocide studies said it would not initiate an investigation at this time. “Dik van der Meulen at [publishing house] Querido is working on a new biography of the prince and we will wait for that before we decide if more research is necessary,” a spokesman told the broadcaster.

The Prins Bernhard Cultuurfonds, originally the Spitfire Fund founded by the prince in 1940 to raise money for arms, said it had been “surprised by the announcement and the existence of the document” and would “consider the consequences”.